The broad objective of this project is to understand the molecular mechanisms by which extracellular signals regulate the intracellular events. Glycogen metabolism, has long been a model for studying such controls which, in mammals, involve hormones such as insulin, glucagon and catecholamines. This project focuses on signalling pathways in the yeast Saccharomyces cerevisiae involved in regulating glycogen metabolism, and especially the enzyme glycogen synthase. In preliminary work, yeast glycogen synthase has been purified and one corresponding gene cloned. The specific aims are: (i) to complete characterization of the yeast enzyme and establish how many glycogen synthase genes are present in yeast. The purified protein contains two related polypeptides, 77 and 85 Kda, and their exact relationship to each other and the glycogen synthase genes (if more than one) is still unknown.; (ii) to identify which sites in the enzyme are phosphorylated in whole cells and to define the corresponding protein kinase(s); (iii) to correlate in vitro phosphorylation of individual sites with changes in enzymic properties; and (iv) to analyze changes in glycogen synthase phosphorylation in response to different physiological situations, incorporating mutants affecting the signalling pathways and mutations, introduced by reverse genetics, in the glycogen synthase itself. The goal is a better molecular understanding of protein phosphorylation and signalling mechanisms in yeast. In turn, such results should provide a broader perspective on intracellular signalling that can be relevant to understanding similar processes in mammals, including control by hormones. The research, though fundamental in nature, is relevant to situations of impaired hormonal control, such as in diabetes.